Re: [PATCH v2] docs: filesystems: document the squashfs specific mount options

[Phillip Lougher]

On 30/10/2023 12:57, Ariel Miculas wrote:
> On 23/10/29 08:33PM, Phillip Lougher wrote:
> > On 29/10/2023 16:19, Ariel Miculas wrote:
> > > When SQUASHFS_CHOICE_DECOMP_BY_MOUNT is set, the "threads" mount option
> > > can be used to specify the decompression mode: single-threaded,
> > > multi-threaded, percpu or the number of threads used for decompression.
> > > When SQUASHFS_CHOICE_DECOMP_BY_MOUNT is not set and
> > > SQUASHFS_DECOMP_MULTI is set, the "threads" option can also be used to
> > > specify the number of threads used for decompression. This mount option
> > > is only mentioned in fs/squashfs/Kconfig, which makes it difficult to
> > > find.
> > >
> > > Another mount option available is "errors", which can be configured to
> > > panic the kernel when squashfs errors are encountered.
> > >
> > > Add both these options to the squashfs documentation, making them more
> > > noticeable.
> > >
> > > Signed-off-by: Ariel Miculas <amiculas@xxxxxxxxx>
> >
> > Looks good to me.
> >
> > Reviewed-by: Phillip Lougher <phillip@xxxxxxxxxxxxxxx>
>
> Unfortunately, it seems this is not quite correct either:
> There is the config option SQUASHFS_MOUNT_DECOMP_THREADS:
> ```
> 	bool "Add the mount parameter 'threads=' for squashfs"
> 	depends on SQUASHFS
> 	depends on SQUASHFS_DECOMP_MULTI
> 	default n
> 	help
> 	  Use threads= to set the decompression parallel mode and the number of threads.
> 	  If SQUASHFS_CHOICE_DECOMP_BY_MOUNT=y
> 	      threads=<single|multi|percpu|1|2|3|...>
> 	  else
> 	      threads=<2|3|...>
> 	  The upper limit is num_online_cpus() * 2.
> ```
> that depends on SQUASHFS_DECOMP_MULTI.
> So I think I should take my v1 patch and specify that the "threads="
> mount option depends on SQUASHFS_MOUNT_DECOMP_THREADS. There's no need
> to specify SQUASHFS_DECOMP_MULTI, because SQUASHFS_MOUNT_DECOMP_THREADS
> already depends on it.

Sorry, you have to specify SQUASHFS_DECOMP_MULTI to be able to specify
SQUASHFS_MOUNT_DECOMP_THREADS if SQUASHFS_DECOMP_BY_MOUNT is unselected.

Just try it, do make menuconfig, ensure SQUASHFS_CHOICE_DECOMP_BY_MOUNT
is unselected, select Single threaded decompression and you won't be
able to specify SQUASHFS_MOUNT_DECOMP_THREADS.

That was the point of my review. What bit don't you understand?

Phillip

> What do you think?
>
> Regards,
> Ariel